Ambiguity Effect

The ambiguity effect is the tendency to avoid options whose probability of a favorable outcome is unknown or unclear, in favor of an option with a known probability, even when the ambiguous option might objectively offer better expected value. The economist Daniel Ellsberg first demonstrated the underlying pattern experimentally in 1961, in what became known as the Ellsberg paradox, showing that people strongly preferred betting on drawing a ball of a known color proportion from an urn over betting on an urn whose color proportions were unknown, in a way that could not be explained by standard expected utility theory. The effect is foundational to the study of ambiguity aversion in behavioral economics and decision theory, and it has been used to explain real-world patterns such as investors preferring familiar domestic assets over unfamiliar foreign ones even when the foreign assets carry comparable or lower objective risk.